Normal microflora vs pathogens

TYPES OF MICROBIAL INTERACTIONS
1. Pathogens
  1. Can cause disease in individuals with normal host defences
2. Commensals
  1. The normal microflora found normally on those parts of the body that are exposed to the external environment
  2. COMMENSALS AS OPPORTUNISTIC PATHOGENS
    1. Transfer to normally sterile areas
    2. E.G. infection of GT
    3. E.G. oral streptococci to heart valves
    4. Damage to epithelium
    5. E.G. staphylococci and pseudomonas burns or wounds
    6. E.G. bacterial pneumonia following influenza
    7. Immune supression
    8. E.G. gut flora septicaemia following radiation
    9. E.G. many pathogens following HIV or immunosuppressive drugs
    10. Antibiotic treatment
    11. E.G. clostridium difficile
3. Opportunistic pathogens
  1. Can cause infection if host defences are impaired
  2. Can often be derived from normal microflora
COMMENSALS OR NORMAL MICROFLORA
1. Organisms that live on or within the body of healthy individuals
2. May be of benefit
TYPES OF SYMBIOSIS
1. Close interactions between organisms
2. At least one organism gains
3. Microorganisms may be harmful to host
4. COMMENSALISM
  1. Neither harm nor benefit the host
5. MUTUALISM
  1. Both organisms benefit
  2. Microbes get a place to live and nutrients
  3. Microbes may be beneficial to host
6. PARASITISM
  1. Host is hormed
  2. Parasite gains
NORMAL FLORA
1. Microbes normally found on healthy individuals
2. Usually harmless
3. Microbiota/microbiome
4. Very abundant
5. More microbes than host cells in body
6. Much smaller in size
7. Transient (impermanent ) microflora
8. DO NOT INJURE HOST BECAUSE
  1. Survive because they are harmless
  2. If they become less fit = kill or be killed
  3. Fail to gain from damaging host
9. MICROFLORA PROTECTS US
  1. Inhibits pathogens
  2. Aids digestive processes
  3. Colonization resistance
  4. Competition for space and nutrients with pathogens
  5. Release of bacteriocins and other antibacterials
  6. Substances to prevent pathogen growth
  7. Stimulation of the immune system
  8. Continued antigenic stimulation from commensals
  9. Cross-reaching protective immunity against pathogens
  10. DETRIMENTAL EFFECTS
    1. Dental caries (toothy decay)
    2. Acne and other skin disorders
    3. Body odour
    4. Ulcers
    5. Conversion of compounds to toxic forms (cancer)
10. FORMATION OF NORMAL MICROFLORA
  1. Foetus is sterile
  2. When born they acquire microflora from mothers vagina (environmental acquisition)
  3. Contact with others
  4. LARGE INTESTINE
    1. Anaerobic environment abundant microbial anaerobic populations
    2. Greatest numbers of normal microflora
  5. Colonization
    1. Colonization of the large bowel occurs in stages
    2. During a vaginal birth lactobactilli are the first colonizers
    3. E.coli soon follows
    4. New born does not start to acquire a complex intestinal fora until weaned
  6. Where do organisms come from?
    1. Oral exposure to faecal microbes
    2. Facultative anaerobes colonise first and strict anaerobes later
    3. Normal flora, mouth
    4. Normal flora, skin
11. CHANGES IN NORMAL MICROFLORA
  1. New organisms may be acquired
  2. Sterile in utero; neonate colonized from mother during birth
  3. Colonization of gut and URT in hospitalised patients (nosocomial infections)
  4. Cross infection with Colostridium difficile, Methicillin resistant Staphylococcus aureus (MRSA) and Vancomycin resistant Enterococci (VRE)
  5. With changes in physiology and development
  6. Gut flora changes after breast feeding and weaning
  7. Female genital tract and lactobacilli
  8. When antibiotics select for a 'resistant flora'
  9. Candida overgrowth in mouth and vagina (thrush)
  10. Clostridium difficile (antibiotic-associated colitis
About 10^12 bacterial cells/gram in gut
1. Only 10^13 in human cells
2. >1kg of bacteria in adult gut
3. >1000 species of bacteria and archaea (many uncultured)
4. Composition of normal flora varies from individual to individual
MICROBIAL PATHOGENESIS
1. Disease
2. Pathogen
3. Virulence (severity)
4. Infection
5. Non communicable
6. Microbial intoxications
KOCHS 4 POSTULATES
1. IDENTIFICATION OF INFECTIOUS DISEASE
  1. 1. The microorganism (pathogen) must be present in all cases of the disease
  2. 2. The pathogen can be isolated from the diseased host and grown in pure culture
  3. 3. The pathogen from the pure culture must cause the same disease when inoculated into a healthy, susceptible laboratory animal
  4. The pathogen must be re-isolated from the new host and shown to be the same as the originally inoculated pathogen
2. MOLECULAR DETECTION: ADAPTING KOCHS 4 POSTULATES
  1. 1. The biochemical or genetic property should always be associated with pathogenic strains
  2. 2. Specific inactivation of the gene that specifies a virulence factor should cause a drop in virulence
  3. 3. Reversion of the mutated gene or allelic replacement by recombination or complementation should restore virulence
  4. 4. Difficulties of defining single 'virulence factors'
VERTICAL DISEASE TRANSMISSIONS
1. Persistance of the agent
2. Transmitted from the parent to offspring
3. Neonatal infection
4. E.G. gonorrhoea, HIV and Zika
5. Infection in utero
6. E.G. rubella and listeria
HORIZONTAL DISEASE TRANSMISSIONS
1. Inhalation of droplets (aerosols)
2. E.G. influenza
3. Faecal-oral
4. E.G. cholera
5. Vector-bone
6. E.G. malaria
7. Sex or blood exchange
8. E.G. HIV

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Normal microflora vs pathogens

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	Created by Eleana Landregan over 5 years ago